For the connection between a FPC and a rigid printed circuit (RPC), a connector and an anisotropic conductive film (ACF) have been used. When the FPC cable is connected to the substrate, it is common to dispose a connector for exclusive use on the substrate, and then connect the FPC cable to the connector. When the FPC cable is connected to the substrate using the connector, a cable terminal portion is covered with a shield layer of the FPC cable and each signal line can be shielded by the connector. Thus, electromagnetic waves leaking from the connection between the FPC cable and the substrate can be eliminated.
In order to reduce the thickness of electronic devices, a FPC cable is sometimes directly bonded to a substrate. For direct bonding, an ACF and solder-in-glue (SIG) are utilized. In SIG bonding, when heat is applied to a connection agent in which fine solder particles are scattered in a thermosetting resin-based adhesive, the fine solder particles melt for solder bonding and the adhesive is cured for electrical and physical bonding. At this time, the fine solder particles are scattered, and therefore an electrical short-circuit does not occur between adjacent different signal terminals.
When an FPC cable in which a shield layer is formed on at least one surface side of a signal layer in which a signal line group is arranged is directly bonded to a substrate, the adhesive described above is interposed between the FPC cable and the substrate, and then a hot bar is pressed against the substrate side from the shield layer side of the FPC cable to melt the solder. The shield layer has high thermal conductivity, and the heat supplied from the hot bar escapes through the shield layer, so that solder connection cannot be ensured, and the shield layer of the connection portion is removed. However, when the shield layer is removed, the shield layer does not present in a connection portion where the shield layer is removed and the solder connection is performed, and electromagnetic waves leak from the connection portion.
Consequently, it would be preferable to provide an improved cable connection structure capable of ensuring the bonding of an FPC cable to a substrate.